Modulating system



D. D. GRIEG MODULATING SYSTEM July 6, 1948.

Filed" July 29. 1944 2 Sheets-Sheet 1 H/@H Pass FM TER PULSE SOI/KCE Vl n.

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MODULATING SYSTEM Filed July 29, 1944 2 sheets-sheet 2 MOM/77716 Patented July 6, 194g Donald D.

New York, N. Y.,

Grieg, Forest Federal Telephone and a corporation of Delaware Hills, N. Y., assignor to Radio Corporation,

Application July 29, 1944, Serial No. 547,122

This invention relates to improvements in modulating systems, and more particularly to novel methods and means for Width-modulating pulses in accordance with intelligence-signifying signals, and is a continuation-in-part of my copending application Serial No. 511,406, filed No; vember 23, 1943.

An object of the present invention is to provide anovel method and means for width modulating a series of normally equal-width pulses for transmitting intelligence.

Another object of this invention is to provide a pulse-width modulating system of improved dynamic range and minimum variation in average power.

Another object of this invention is to derive from a pulse shock-excited circuit, a series of variable width pulses modulated in accordance with predetermined intelligence to be transmitted.

These and other objects, capabilities and advantages of the invention will appear from the subjoined detail description of one embodiment and a modification thereof, illustrated in the'accompanying drawings, in which:

Fig. 1 is a circuit diagram, partially in block form, of a preferred form of pulse-width modulating system in accordance with the present invention;

Fig. 2 is a diagram illustrating by way. of example the time relation between a series of un- 20 claims. (c1. 17a-171.5)

additional impedance across the tuned circuit 2 the tuning of the circuit 2 within certain predetermined limits. In this embodiment, the tube 4 provides a resistance varying in step with the modulating signal across the tuned circuit which serves to vary the resonant frequency thereof by well known laws. Since the tube' il is parallel to the resistor R with respect to the tuned circuit 2, there will exist a modulation component across resistor R. The resistance R. is selected high relative to the resistance of the tube 4. `By passing the output from the tuned circuit 2 through a high-pass filter ii, the low modulating frequency components produced across resistor R are removed. The output of lter 6 is passed through a suitable shaper and amplifier 1 for the purpose `of re-shaping the pulses into the rectangular pulses, which, if desired, may be further shaped by differentiation and inversion at 8 into narrow pulses corresponding in time to the leading and trailing edges thereof. p t

In Fig. 2, curve A represents a series of equally spaced, equal-width rectangularpulses a to :i inclusive, produced by the pulse source l and applied to the resonant circuit 2. Thepulses of source I however, may be of variousshapes so long as they present one edge, either leading or modulated pulses, a modulating wave and the resultant width-modulated pulses according to the system illustrated in Fig. 1;

Fig. 3 is a circuit diagram, partially in block form of a modied form of pulse-width modulating circuit;

Fig. 4 is a diagram similar to Fig. 2, illustrating the mode of operation of the system shown in Fig. 3.

The iorm of my invention shown in Fig. 1 includes -a voltage source l of any known type which has a relatively abrupt potential change characteristic. A suitable form illustrated is one which produces substantially rectangular pulses such as a, b. This series of pulses is applied to a resonant circuit 2 across which is connected a rectifier 3 whose purpose is to limit the undulations resulting from shock excitation of the circuit 2 to the rst, primary undulation oi one polarity. Also in eiiective shunt with the resonant circuit 2 is connected a reactance circuit including tube 4 Whose control grid, in turn, is energized by a modulating voltage source 5. t As is well known in the art, the tube 4 presents an trailing, that follows a given timing as will be further explained hereinafter. This circuit 2 will have a normal resonance4 frequency which will be varied by the operation of the tube 4 in accordance with some modulating source indicated by way of exampleby the voltage Wave B. If it is yassumed that the normal resonance frequency of the tuned circuit 2 occurs at maximum negative modulating voltage, the resonant frequency will then vary between limits as determined by theimaximum positive and negative points on the modulating voltage curve.

The series oi waves indicated at C, Fig. 2, illustrates the first undulations which appear from the output of the resonant circuit 2 upon shock excitation o` the latter from the series of applied pulses a. to i. y It will be noted, for example, that the resulting pulses a1, e1, and 71 will all be oi equal width since these `pulses represent the first undulations of theMshock-excited circuit which take place when the modulating voltage controlling the tube `I is at zero value. As the modulating voltage increases, `lioweventhe tuning of the shock-excited circuit 2 varies so that theirst Vundulations produced will be of slightly greater vnegative undulation lfollow undulation 01. inatesthe'negative -undulationrwhichwould be I caused by -theL-trailing-edge of the-original recthe trailing -case would tive-modulationfcr following the-positivelunduladuction ofpulses of porated in Fig. 3 aY closed in'my copending application aboveereferred then applied to "a high f the-output of which is connected tothe -resonant the modulating voltage wave is the widest modulation produced. Conversely, as the modulating voltage decreases, the pulses decrease in width, for example, oli will be of the sarne width as b1, and as thekmodulating voltage curve changes to an increasing negative value the pulsesbecome increasingly narrower so that f1 is narrower than ei, and g1 at. the .maximum negative 'value is the narrowest'pulse of all. As the modulating voltage curve rises, the pulses again increase in width as indicated by undulations h1 and 7'1. Theundul'ations ai to iii, after passingfthroughf .the f' shaper and amplifier l, may V sired, into rectangular pulsesoz'to1 i2 inclusive, of the same spacing as th'epriginall pulseso. to-ff respectively, but of varying width' '1e modulating voltage applied from v:thesource upon the reactance tube ll. These final modulating rectangular pulses may, if desiredandas previously explained, be differentiated into narbe rcshaped, if derovv pulses a3, yaa, etc.,` corresponding. tothe respective leading-andi trailing'` edges.

tangular pulses;A Ifor example, ther negative .un-

edge of `pulse '-A-and-.the negative un- 1 which would `otherwise result I from edge of thefpulsecand'which in this start simultaneously/'1 with `the negadulation C tion c1.

-Itv will'fthusbe seenfthat AI--fhave @provided a simple pulse-width modulating system producing, either-forfdirecttransmissionpurposes orV for v`a-n'RF carrier modulating potential; v1c ulse's'wloich -will be of substantiallyrequal:amplitude and which are modulated iii-Width according to intelligence or other signalling modulating source.

' In the vevent that theforiginal rectangular pulses are' relative narrow', thereby preventing the prof greater '-widtl`1,7Ik have incorso-called edger i circuit disto. For example, in Fig. 3 I havedisclosed apulse source I' which-may produce relatively narrow pulses lc, l, etc.r These pulses are rst dilerentiated by the lcondenser Aresistor''-olilerentiating circuit 9 andapplied tothe 'fedger circuit l0 which'includes'the triode il. Producedin Vthe output ofthe circuit4` Illv in' the-negative'sense',

are pulses having a relatively straightleading edge and an 'asymptotic Atrailing' edge #For the circuit `shown theseuesultingV negativev4 pulses are preferably passed" through a phase Ireverser l2 producing positive edger pulses indicated, for example, at lc', l', etc.' These edgermpulsesare 'plate impedance tube I3,

circuiti. A rectiflert is connected;- as inl Fig. 1 (except for the reversal of the-plate-and cathodel connections), in shunt with the resonant circuit 2 and the tube l is controlled from the modulating voltage source 5. The pulses derived from the shock-excited resonant circuit 2 are passed through the lter 6 and may be re-shaped in the shaper and amplifier l. it will be noted, however, that the tube il is connected, in effect, di-

`rectly to the resonant circuit 2, thus substanof diagrams the of the resonant circuit 2 'modulation componentswhicn are filtered out at 1 6 may be omitted tion components tially eliminating the component modulation present across resistor R of Fig. 2. The low impedance however, still presents 6. Where the circuit 2 has a high Q the lter since in that case the modula- Will be negligible.

i" In Fig. Ll, I have roughly indicated by a series action which takes place in theA modulating circuit illustrated in Fig. 3. It will be wseenvthat a series of narrow rectangular pulses,

. formed by the edger f into Wider .edger leading edges will shock excite avoided by the pulses into edger taneous value such as indicated at lc to s inclusive are transand phase reverser circuits pulses 7c to s' inclusive, whose the resonant circuit I2 to produce, corresponding tothe instanof the modulating wave, initial undulations k1 to si, respectively. Therectifier tube 3 prevents positive undulations following the desired negative undulations but the problem` l of negative undulations resulting from the sharp trailing edges of rectangular pulses 7c to s is transformation of the rectangular pulses having an exponential trailing edge. Since it may be desirable, or even necessary, to have the resulting undulations produced by shock excitation of the resonant cir- 'cuit of a width greater than the Width of the tions that would otherwise be made possible by the original pulses, it will be clear that such result is edger pulse feature of my invention. It is by this edger pulse feature that I eliminate the production of negative undulaproduced by the r'-trailing edges of the input rectangular pulses.

less than the rst undulation,

cause Variations in the normal -tive lundulations. -cated by negative For example, if the input pulses were of a width the negative undulation resultingfrom thetrailing edgevvould shape ofthe posi- Such adverse effect isindivundulations k1. and the resulting positive undulation x1, curve D, Fig. 4, Where pulse K is `used asthe shock exciting pulse.

pulse source of relatively nar- Vwrowvpulses my invention produces Width-modulated pulses ofagiven shapecharacteristic.

From the foregoing description, it will be readily -apparent that the resonant circuit 2 may be 1 shock-excited by various pulse shapes uother than rectangular and edger pulses so .long as the vv rpulseshapes present shock-exciting vedges of a -ment with the tuning givenpolarity and of sufficiently abrupttpotential change, timed according to a pattern inagreelimits of the circuit. The

. .timing of the shocks need not beregular but may lbe at `uneven intervals solong as they are sufficiently frequent to provide a sumcient number of output pulses to adequately define the modulating intelligence.

It `will also be apparent tothose. skilled in the art that the undulation pulses of curve, C, Fig. 2,

- and curve AD,

` Inv -factg Fig. 4, may be used .directly to modulate a carrierfor transmission purposes.

. comprising a source steps of varying .ing in combination,

Atermined resonant frequency,

. pulses, dampening means lcircuit for eliminating substantially al1 but the .rst undulation thereof after each excitation,

' voltage, and means from said shock-excited tuned circuit to substanf' t-noise ratio of the undulation pulses, however, will be lower than for the `rectangularpulses. The narrow pulses of curve E, Fig. 2, produced by differentiating the rectangular pulses will serve as modulation pulses for purpose of transmission better than the` rectangular pulses without increasing the band width required and with reduced transmitter power requirements.

While I have described above the principles of my invention in certain specific examples, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope thereof asset forth in the objects and in the accompanying claims.

I claim:

1. Pulse-width in combination,

modulating system comprising, means producing a series of voltage pulses, each pulse having at least one abrupt potential change, a tuned circuit having a predetermined resonant frequency, means shock-exciting said tuned circuit by the abrupt potential change of each pulse, dampening means connected to said tuned circuit for eliminating all undulations thereof except the `first one caused by said abrupt potential change, and means varying the width of said first undulations, of modulating voltage, and variable means controlling the tuning of said circuit to alter its resonant frequency in response `to the instantaneous value of said modulating voltage.

2. The combination according to claim 1, in combination with means connected to said tuned circuit for producing a pulse from each first undulation having a width corresponding to the width at a given level on said first undulations.

3. The system according to claim 1, in which said pulse producing means includes means for producing pulses having two abrupt potential changes spaced apart with a Width equal to the width ofthe widest undulations of the tuned circuit, and means shock-exciting said tuned circuit by one of said abrupt potential changes.

4. The system according to claim 1, in which said pulse producing means includes means for producing pulses having two abrupt potential changes spaced apart with a width less than the width of the narrowest undulations of the tuned circuit, means shock-exciting said tuned circuit by one of said abrupt potential changes, and means correcting the other abrupt potential change to a gradual potential change.

5. In a system of the type in which a tuned circuit is shock excited by a series of pulses, the

the tuning of this circuit corresponding to intelligence to be transmitted, pro- -ducing a series of pulses from the oscillations produced in said shock excited circuit, and varying the width of said produced pulses in accordance with the tuning of said circuit.

6. A pulse-width modulating system comprisa source of recurring pulses -of substantially constant Width, a source of modulating voltage, a tuned circuit having a predemeans shock-exciting said tuned circuit in response to said recurring connected to said tuned variable means controlling the tuning of said circuit to alter its resonant frequency in accordance with the instantaneous value of said modulating transforming the undulations i resonant frequency,

tially rectangular pulses whose width corresponds to th-e width of the respective undulation.

7. The combination accOrdingVto claim 6in which said last means comprises an output' circuit including a low-pass filter and a shapercircuit connected to said tuned circuit;

8. The combination according to claim 6, in which said variable tuning means comprises an electronic tube in shunt with the said tuned circuit, and means controlling said `tubefrom said source of modulating voltage; i

9. Pulse-width modulating system comprising, in combination, a source of recurring substantially rectangular pulses of substantially constant width, a tuned circuit having `a lpredetermined means shock-exciting said tuned circuit by said recurring pulses to produce undulations whose width is dependent upon the resonant frequency of the circuit, dampening means connected to said tuned circuit forelimi' nating substantially all but the first undulation thereof after each excitation,v means re-shaping each first undulation into a substantially rectangular pulse of a width corresponding to the `width of the undulation, and controllable means varying the resonant frequency of said tuned circuit to vary the width of the undulations and the pulses derived therefrom. i i

1.0. The method of pulse-width modulation, which comprises the `steps of producing `oscillatory energy in response to aplurality of recurring pulses of at least a given width, eliminating all undulations of the oscillatory energy except the first, producing a series of substantially rectangular pulses having a width corresponding tothe Width of the respective rst undulations, and varying the frequency of said oscillatory energy to correspondingly vary the i width' -of 'said rst undulations.

11. Pulse-width modulating system comprising, in combination, a sourcehof recurring substantially rectangular pulses of'rsubstantially constant width, means transforming said rectangular pulses into pulses having one substantially vertical leading edge and a gradually downwardly curving trailing edge, a tunable circuit having a predetermined resonant frequency, means shockexciting said circuit by said transformed pulses, dampening means connected to said circuit for eliminating substantially all but the first undulation `thereof after each excitation, a source of modulating voltage, means varying the tuning of said circuit in accordance with said modulating voltage to produce undulations of varying width, and means transforming the undulations from said shock-excited circuit into substantially rectangular pulses of a width determined by the width of the successive undulations.

12. The combination according to claim 11, in which said last means comprises an output circuit including a low-pass filter and a shaper circuit connected to said lturnable circuit.

13. The combination according to claim 11, in which said variable tuning means comprises an electronic tube in shunt with the said tunable circuit, and means controlling said tube from said source` of modulating voltage.

14. Pulse-width modulating system comprising, in combination, a source of recurring substantial- 1y rectangular pulses of substantially constant width, means transforming said rectangular pulses into pulses having one substantially vertical leading edge and a gradually downwardly curving trailing edge, a tuned circuit having a predetermined resonant frequency, means shock- -eiicitingsai'd'tixned ,circuit .from said transformed recurring-:pulses'fto Vproduce undulations Whose width -is :dependent upon the resonant frequency `of .the circuit,fdampening means connected to .said tuned circuit -for eliminating substantially all but the rst undulation'thereof after each excitatiomfmeans=reshaping each rst undulation linto afsubstantially rectangular pulse of a width corresponding to .the width of the undulation,

and controllable means varying the resonant frequency of said tuned-.circuit `to vary the Width of fthe-'first undulations'and the pulses derived therefrom;v

l15.A yPulseewidtn ymodulating system comprising,

'in -.combin'ation,a source oie-recurring, relatively narrow,v .substantially rectangular pulses of substantially: constantpwidth, -means transforming said/narrow rectangular `pulses into wider constant-.width pulses having one substantially ver- .tical/.leading iedge and a gradually downwardly -curvir-ig.trailingedge,- a tuned circuit having a predetermined-resonant frequency, means shockexciting.; said-tuned circuit by said transformed pulses, dam-pening-means connected to said tuned circuitfor veliminating substantiallyl all but the rst'undulation thereof after each excitation,y a source xof )modulating voltage, vmeans -varyingthe tuning of said circuit in l.accordance with said modulating Voltage to produce undulations of varyingwidtnfand'means transforming each rst undulationifromisaid,shock-excited circuit into a substantially:rectangular .pulse of a Width determinedby theiwidthof tlieA corresponding undulation.

16.1 'Il'ieimethodiofipulse modulation, which in- `cludesfthefsteps:of-producing a series of relatively -narrow rectangular rpulses of substantially constantwidtnproducing a corresponding seriesvof Wider pulses each having a substantially vertical leading edge and yan asymptotic trailing edge, translatingv energy ofsaid last series of pulses into oscillatory energy, eliminating allv undulations of theoscillatory. energy-except the rst, producing a ,series-of substantially vrectangular .pulses having r19. `The;modulatingsystem according Yto claim 1.7. :further inciudineimeans forashapine said :first undulatiollsciojproduepulseszofrapredetermined form :modulatc dj;inywidthr accordinggtozvariations inthezfbase 'Width;- of saidffundulations.

20. Themodulatingisystem according to claim 17, whereinV said means togproducefoscillatory energyfincludesa resonant circuit and said means `to vary thefrequency of saidoscillatory energy includes vmeans-for controlling the resistance in said tuned circuit.

DONALD D. GRIEG.

REFERENCES CITED v-The vfollowingireferences are-of record inthe file .of this patenti UNITED :STATES PATENTS Number Name` Date 2,063,025- Blumlein Dec. I 8, 1935 2,153,202. Nichols Apr. 4, `1939 .2,181,309 Andrieu NOV. 28, 1939 2,284,401 .Manley et al, May 26, 1942 2,289,564 kWrathall July 14, 1942 

